Fully variable valve train

Paul Boughton

The Schaeffler Group has developed a fully variable, cam-actuated, electro-hydraulic valve train, which could be ready for full series production as early as Spring 2009

Engineers at the Schaeffler Group's Engine Systems division have developed a fully variable valve control system which, in tests, has reduced fuel consumption by 10 per cent compared with conventional valve train systems. A significant reduction in diesel engine NOx emissions is also achieved, as well as improved engine response and torque.

The INA 'UniAir' (Universal Air) system is a cam-actuated, electro-hydraulic valve train system, which is supplied by the vehicle's existing engine oil circuit. The system can be used in both petrol and diesel engines.

Engineers at Schaeffler are currently testing UniAir on a prototype passenger car - based on an Opel Vectra with a two-litre, four-cylinder diesel engine (218Nm at 4,000rpm) - which has already successfully achieved more than 20,000km.

The test vehicle has so far achieved a 10 per cent reduction in fuel consumption compared with a car equipped with a standard valve train. The car also meets Euro 4 exhaust gas regulations standards.

On internal combustion engines, UniAir can be installed with throttle-free, continuous software-based load control across the entire engine mapping range.

Using UniAir in diesel engines, the combustion chamber temperature can be accurately controlled by regulating exhaust gas recirculation. At the same time, the effective compression ratio within the cylinder varies, ensuring homogenous combustion of the fuel. Optimising the combustion temperature and the compression ratio in the cylinder enables the production of NOx emissions to be reduced significantly. In addition, costly exhaust treatment is eliminated.

Optimising charge cycles in valve switching systems has already been achieved with partially variable valve trains, for example by using two-stage switching systems with switchable tappets. The first generation of partially variable valve train systems was followed by the first fully variable production valve train in 1999, using BMW's 'Valvetronic' system. During part-load operation, such as idling, the cylinder charging was controlled using the valve lift of the inlet valves and the opening period. The phasing of the inlet and outlet camshafts was driven by a variable camshaft timing system.

But the INA UniAir system represents a step-change in variable valve train systems. The system can provide full coverage of every conceivable airflow possibility, from zero valve lift to maximum lift, dictated by the camshaft lobe for each individual cylinder or valve. With the de-throttling of the engine, UniAir can provide early intake-valve closing or late intake-valve opening, to maximise engine breathing relative to certain engine speed and load conditions.

UniAir can offer valve lift events for every valve - individually and cycle-to-cycle. In contrast, an electromechanically actuated, fully variable valve train requires several cam events to achieve the same lift differential.

In addition to the 10 per cent reduction in fuel consumption, a further 1 to 2 per cent can be achieved by increasing the compression ratio, as 'knock' limits can be optimised. Further fuel efficiency gains can be made by applying cylinder de-activation strategies, which require a deactivating element on certain exhaust valve locations.

For more information, visit www.schaeffler.co.uk


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